Microcontroller based resolver-to-digital converter

Abstract

Disclosed is a microcontroller based Resolver-to-Digital converter in which synchronous sample-and-hold type demodulation is used with an optimum time of the sample-and-hold established by control of the phase and the magnitude of the reference voltage supplied to the resolver as a function of the resolver's electrical characteristics, thus minimizing the quadrature and the even harmonics effects which are a byproduct of the resolver. The demodulated resolver outputs are filtered and are converted to digital form with the use of an A/D converter integral or external to the microcontroller. The magnitude of the reference voltage is set to an optimum value in order to utilize the full range of the A/D converter. Using digital signal processing techniques and known trigonometric identities the shaft angle of the resolver is extracted from the A/D outputs and supplied to the output latches in continuous or bus controlled fashion. This method is further expended to cover the use of the R/D converter with multiple resolvers.

I claim: 
     
       1. A resolver-to-digital converter comprising: a resolver having a reference winding and first and second output windings;   a microcontroller having an A/D converter and a high-speed input/output section having first through third high-speed inputs and first and second high-speed outputs, said microcontroller generating at said second high-speed output a reference square wave having a selected frequency;   a shaping filter receiving said reference square wave and in response generating an initial sine wave which has the same selected frequency but is delayed in phase relative to the reference square wave, and a modulating circuit which receives said sine wave, applies a selected modulation thereto to generate a reference sine wave and drives said reference winding of said resolver with said reference sine wave to thereby cause said first and second winding to output respective first and second optput waves which have said selected frequency but are delayed in phase relative to said reference sine wave;   a first detection circuit detecting the crossing of a selected reference by said first output wave and supplying information regarding said crossing to said first high-speed input of said microcontroller, a second detection circuit detecting the crossing of a selected reference by said second output wave and supplying information regarding said crossing to said second high-speed input of said microcontroller, and a third detection circuit detecting the crossing of a selected reference by said reference sine wave and supplying information regarding said crossing to said third high-speed input of said microcontroller;   first and second sampling circuits which sample said first and second output waves, respectively, and supply respective samples to said A/D converter of said microcontroller for conversion thereof into digital values;   wherein said microcontroller uses said information supplied thereto at said first through third high-speed inputs to compute the phase delay of said first and second output waves and to provide at said first high-speed output a sampling signal applied to said sampling circuits to cause said sampling circuits to sample said first and second output waveforms at or about the 90 degree point and provide the resulting samples to said A/D converter, to thereby avoid or reduce quadrature and second harmonic effects.   
     
     
       2. A resolver-to-digital converter as in claim 1 in which said microcontroller has a control output coupled to said modulating circuit and is responsive to said samples to provide at said control output a control signal causing said modulating circuit to adjust the amplitude of said reference sine waveform such that the amplitude of the greater of said first and second output signals matches the dynamic range of said A/D converter. 
     
     
       3. A resolver-to digital converter comprising: a resolver having a reference winding and first and second output windings;   a microcontroller circuit comprising an A/D converter and a high-speed input/output section having first through third high-speed inputs and first and second high-speed outputs, said microcontroller circuit generating at said second high-speed output a reference square wave having a selected frequency;   a processing circuit receiving said reference square wave and in response generating a reference sine wave which has a known frequency and a known phase relative to the reference square wave and driving said reference winding of said resolver with said reference sine wave to thereby cause said first and second winding to output respective first and second output waves which conform to said known frequency but differ in phase from the reference sine wave;   a detection circuit detecting the crossing of a selected reference by at least one of said first and second output waves and supplying information regarding said crossing to respective one of said first and second high-speed inputs, and a third detection circuit detecting the crossing of a selected reference by said reference sine wave and supplying information regarding said crossing to said third high-speed input;   first and second sampling circuits which sample said first and second output waves, respectively, and supply respective samples to said A/D converter of said microcontroller circuit for conversion of said samples into digital values;   wherein said microcontroller circuit comprises circuits using the information supplied to said first and/or second high-speed input and to said third high-speed input to compute a time interval related to a phase difference between at least one of said first and second output waves and said reference sine wave and to provide at said first high-speed output a sampling signal applied to said sampling circuits to cause said sampling circuits to sample said first and second output waveforms at or about the 90 degree point and provide the resulting samples to said A/D converter.   
     
     
       4. A resolver-to-digital converter as in claim 3 in which said microcontroller circuit comprises a single-chip microprocessor. 
     
     
       5. A resolver-to-digital converter as in claim 4 in which said processing circuit comprises a shaping filter which converts the reference square wave ito a sine wave. 
     
     
       6. A resolver-to-digital converter as in claim 5 in which said processing circuit comprises a modulator which applies a selected modulation to the sine wave into which the shaping filter converts the reference square wave in order to generate said reference sine wave which drives said reference winding, said modulation causing the output sine waves to match the dynamic range of the A/D converter. 
     
     
       7. A resolver-to-digital converter as in claim 6 in which said detection circuit includes a respective detection circuit for detecting when each of the first and second output waves crosses the reference and for supplying information regarding the crossing of the reference by the first output wave to the first high-speed input and for supplying information regarding the crossing of the reference by the second output wave to the second high-speed input, and wherein the microcontroller circuit uses information from both of said first and second detection circuits to compute said time interval related to said phase difference. 
     
     
       8. A resolver-to-digital converter as in claim 7 including a number of separate resolvers, each having a reference winding and first and second output windings, and including a circuit for successively connecting each resolver to said microporcessor circuti to compute and store respective time intervals related to the phase differences pertaining to the respective resolvers, and wherein said microporcessor circuit uses said stored time intervals to generate respective sampling signals to sample the first and second output waves of the respective resolvers at or about the respective 90 degree points of said output waveforms. 
     
     
       9. A resolver-to-digital converter as in claim 3 in which said processing circuit comprises a shaping filter which converts the reference square wave into a sine wave. 
     
     
       10. A resolver-to-digital concerter as in claim 9 in which said processing circuit comprises a modulator which applies a selected modulation to the sine wave into which the shaping filter converts the reference square wave i order to generate said reference sine wave which drives said reference winding, said modulation causing the output sine waves to match the dynamic range of the A/D converter. 
     
     
       11. A resolver-to-digital converter as in claim 10 including a number of separate resolkvers, each havign a reference winding and first and second output windings, and including a circuit for successively connecting each resolver to said microprocessor circuit to compute and store respective time intervals related to the phase differences pertaining to the respective resolvers, and wherein said microprocessor circuit uses said stored time intervals to sample the first and second output waves of each of said resolvers at or about the respective 90 degree points. 
     
     
       12. A resolver-to-digital converter as in claim 3 including a number of separate resolvers, each having a reference winding and first and second output windings, and including a circuit for connecting the resolvers to said microprocessor circuit to compute and store respective time intervals related to the phase differences pertaining to the respective resolvers, and wherein said microprocessor circuit uses said stored time intervals to sample the first and second output waves of each of said resolvers at or about the respective 90 degree points. 
     
     
       13. A resolver-to-digital converter as in claim 3 in which said processing circuit comprises a modulator which modulates said reference sine wave to cause the output sine waves to match the dynamic range of the A/D converter. 
     
     
       14. A resolver-to-digital converter as in claim 3 in which said resolver has a shaft and including a circuit using said digital values of the samples of said output sine waves to compute the angular position of the resolver shaft and to utilize the computed angular position. 
     
     
       15. A method comprising: providing a resolver having a reference winding and first and second output windings;   generating a reference square wave having a selected frequency;   converting said reference square wave into a reference sine wave which has a known frequency and a known phase relative to the reference square wave and driving said reference winding of said resolver with said reference sine wave to cause said first and second windings to output respective first and second output waves which conform to said known frequency but differ in phase from the reference sine wave;   detecting the crossing of a selected reference by at least one of said first and second output waves and the crossing of a selected reference by said reference sine wave and generating information regarding said crossings;   using the information supplied at said at least one of first and second high-speed inputs and at said third high-speed input to compute at least one time interval related to a phase difference between at least one of said first and second output waves and said reference sine wave;   utilizing said time interval to generate a sampling signal related to about the 90 degree points of said output sine waves; and   sampling said first and second output waves in accordance with said sampling signal and converting the samples into digital values.   
     
     
       16. A method as in claim 15 including modulating the reference sine wave to cause the output waves to match the dynamic range of the A/D converter. 
     
     
       17. A method as in claim 16 in which the detecting step comprises detecting the crossing of a selected reference by each of said first and second output waves and generating information regarding said crossings, and the using step comprises using information regarding the crossing of the reference by each of said output waves to compute said at least one time interval related to said phase difference. 
     
     
       18. A method as in claim 17 in which the providing step comprises providing a number of separate resolvers, each having a respective reference winding and respective first and second output windings and sequentially applying said detecting and using steps to the output waves of the respective resolvers in order to compute respective time intervals related to phase differences pertaining to the respective resolvers, and storing said time intervals and applying said utilizing and sampling steps to the respective resolvers by using said stored time intervals to sample the first and second output waves of the respective resolvers at or about the respective 90 degree points of the respective output waves. 
     
     
       19. A method as in claim 15 in which the detecting step comprises detecting the crossing of a selected reference by each of said first and second output waves and generating information regarding said crossings, and the using step comprises using information regarding the crossing of the reference by each of said output waves to compute two time intervals related to phase differences. 
     
     
       20. A method as in claim 15 in which the providing step comprises providing a number of separate resolvers, each having a respective reference winding and respective first and second output windings and sequentially applying said detecting and using steps to the output waves of the respective resolvers in order to compute respective time intervals related to phase differences pertaining to the respective resolvers, and storing said time intervals and applying said utilizing and sampling steps to the respective resolver by using said stored time intervals to sample the first and second output waves of the respective resolvers at or about the respective 90 degree points of the respective output waves.